This invention relates to turbo machinery and, specifically, to a new variable stator vane construction for a turbine compressor and related method for removal of existing variable stator vanes an d replacement with the new vanes, without having to remove the turbine rotor.
Axial compressors used in gas turbines of the assignee""s product line may include as many as eighteen (18) stages, each comprising a bladed disk. In addition, a circumferential array of variable guide vanes are provided at the compressor inlet. The latter serve to adjust the airflow at start-up and provide higher firing temperature at reduced load for regenerative-cycle and combined-cycle applications. These inlet guide vanes are gear actuated from outside the inlet casing, using an annular drive ring, a geared rack, and a drive gear to turn the vanes in unison during operation.
Specifically, the inlet guide vanes are supported in two semi-annular halves, referred to herein as the upper and lower inlet casings. In the illustrative example, four inlet guide vanes are supported in each of eight support segments bolted to the lower inlet casing. While removal and replacement of the inlet guide vanes in the upper inlet casing can be accomplished relatively easily while the upper inlet casing is removed, removal and replacement of the inlet guide vanes in the lower inlet casing, without removal of the rotor, is problematic, due primarily to the extended axial length of the vanes. The latter is necessitated by the requirement that the vane adjustment drive be located outside the casing. Thus, each of the vanes have an integral, extended drive stem that extends through the casing where it mounts the drive gear for engagement with the annular geared rack fixed to the annular drive ring. Removal of the rotor has been required to create the necessary space to remove these extended vanes. The process, however, is complex, time consuming and expensive.
This invention relates to a technique for removing conventional inlet guide vanes, and to a new replacement inlet guide vane assembly that allows reinstalling of the inlet guide vanes in the lower half of the inlet casing, both removal and reinstallation achievable without removing the rotor.
Removal of a conventional inlet guide vanes in accordance with this invention involves removing the external drive gears from the guide vanes in the lower inlet casing, and then cutting the vanes, allowing both cut pieces of each guide vane to be removed from inside the lower inlet casing. This removal procedure is followed for the inlet guide vanes mounted in each of the support segments in the lower inlet casing, segment by segment. Installation of replacement inlet guide vanes without removal of the rotor requires modification of the existing inlet guide vane design, as described further below.
The radially outer, or drive end, of each guide vane will now include a multi-piece drive stem assembly. The shortened radial length of the guide vane stems enables each guide vane to be manually located within the casing, while the additional hardware, including an intermediate jack shaft, drive gear and outer stem piece, may be assembled from outside the inlet casing. That portion of the drive stem integral with the vane has been radially shortened and is provided with splines and flats that mate with a complementary recess in the intermediate jack shaft. The other end of the jack shaft slidably receives the drive gear. An outer stem piece is adapted for installation on the free end of the jack shaft, projecting beyond the drive gear, again with torque-transmitting flats (or hex-shaped head or similar). A radial screw extends from the outer stem piece through the jack shaft, and is threadably receivable in the vane stem, for loosely holding the components together. After all of the vanes are adjusted to the appropriate vane angle, the radial screws are tightened and the outer stem pieces are welded to the drive gear, thus creating a torque transmission path between the drive ring, geared rack, drive gears and the guide vanes.
Thus, in one aspect, the invention relates to a method of replacing an inlet guide vane from a lower inlet casing of a compressor, the lower inlet casing adapted to be secured to an upper inlet casing at a horizontal joint, wherein the inlet guide vane is supported between radially inner and outer walls of the lower inlet casing, and further wherein the inlet guide vane is formed with an integral stem that extends radially through the outer wall and supports a gear on its outer end that engages an annular gear rack, the method comprising:
a) removing the gear of the radially outer end of the integral stem of the inlet guide vane;
b) shearing the inlet guide vane into two cut portions;
c) removing the cut portions of the inlet guide vane from inside the lower inlet casing; and
d) replacing the inlet guide vane by a modified inlet guide vane having a two-piece stem assembly that enables installation without removal of the rotor.
In another aspect, the invention relates to an adjustable inlet guide vane assembly comprising a vane having a cylindrical stub at a radially inner end thereof and a relatively short integral extension stem at a radially outer end thereof; a jack shaft adapted for connection at a radially inner end thereof to a radially outer end of the integral stem such that torque applied to the jack shaft is transmitted to the vane, a radially outer end of the jack shaft adapted to receive a drive gear.